Electric cable



Nov. 8,l 1927.

S. C. CAWTHON Filed June 27. 1925 MUM /n Ven 70/ Jmae/W/a Patented Nov.8, 1927.

UNITED STATES 1,648,443 PATENT OFFICE.

SAMUEL CLIFTON CAWTHON, OF WESTERN SPRINGS, ILLINOIS, ASSIGNOR TO WEST-ERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OFNEW YORK.

ELECTRIC CABLE.

Application led .Tune- 27, 1925. Serial No. `39,886.

This invention relates to electric cables, and more particularly toimprovements in submarine cables and methods of making them.

In one type of submarine cables a plurality of conductors having paperor similar fibrous insulation are stranded together to form a cable corewhich is thereafter sheathed with a metal sheath, such as a lead alloy,preferably applied thereto in a substantially solid state by anextrusion press. This protective sheath is of great importance insubmarine cables since it forms a seal for the core against thelentrance of water. It has been found in practice that the more nearlycontinuous the operation of extruding the lead sheath around the corewith a minimum of interruption in the operation of the prelss the moreetiicient and durable is the sea The usual practice in making submarinecables having paper or similar fibrous insulation is to provide arelatively large amount of insulation which is compressed as much as ismechanically possible without injuring the insulation during thestranding process. This compact form is used in order that as muchresistance as possible may be offered to the flow of water in the eventof a break in the sheathing and that the cable may be taken up andrepaired before a substantial length thereof is ruined.

It has been suggested that by inserting plugs at intervals inunder-water cables, the same effect can be obtained. The value of a pluglies chiefly in the fact that with its use a much more efiicient cablemay be designed and constructed, for except at the actual pluggingpoint, the cable may be made much less compact and therefore moreefficient from a transmission standpoint than the type above mentioned.The cable can also be made with less insulating paper and of smallerdiameter than is ordinarily possible.

The primary object of this invention is to produce a submarine cablehaving an im.- proved plug of this type the efficiency of one portion ofwhich increases upon the failure of another portion, upon a breakoccurring in the cable, to positively seal the adjacent portion of thecable from the entrance of water.

Another object is to produce a plug of this type wherein the method offabrication is such that it permits the subsequent sheathing ofthe.cable core to be accomplished with a minimum of interruption in theoperation of .the extrusion press, in consequence of which a moredurable and efiicient sheath is produced.

'In accordance with the general features of this invention, a section ofthe stranded cable core is first treated with a relatively thinwater-proofing compound which will thoroughly impregnate and water proofthe paper insulating material. The section is then subJected to arelatively heavy water proofing compound which will fill all theinterstices between the individual strands constituting the core.Thereafter the impregnated section is bound very tightly by an elasticrubber tape for a portion of its length then loosely for anotherportion, and then tightly again for the balance of the impregnatedsection. A wrapping of strand. for instance, a cotton thread is thenapplied with sufiicient tension at the beginning and ending of eachbound portion of the impregnated section. The cable core is theninserted in a suitably heated baking oven for a suitable period toremove any moisture which may be contained in the insulation of thecable core. Thereafter the diameter of the bound section is built up tothe diameter of the adjacent portions of the cable core with a materialof such a character that the heat of the lead covering when applied issufficient to cause the material to flow into a homogeneous mass tocompletely fill the space between 'the core and the sheath.

Where plugs are inserted in a cable as hereinbefore mentioned, onemethod has been to bind a section of the cable core which has beenpreviously impregnated with `a waterproofing compound having acomparatively low flow point with elastic rubber tape to give it areduced diameter at a single portion of the impregnated section`I sothat upon the subsequent binding thereof it will provide a certaindegree of flexibility. This has the disadvantage that the impregnatingcompound at the baking temperature will tendy to flow from the center ofthe plug or the reduced portion toward either end and into otherportions of the cable on account of the low flow point thereof, therebyreducing the effectiveness ofthe plug. If the plugs are inserted afterthe baking operation and during the covering of the cable core with alead Sheath, for instance, the time of inserthe press is idle andconsequently the outputv the accompanying drawing, in whichconductorsllO are covered in the usual manner with paper insulatingmaterial. A section 11 of the cable core, preferably of from twelve totwenty-four inches in lengthisimpregnated with water-proofing compoundsof the type fully described in copending application of F. S. Malm,Serial No. 630,201, filed April 6, 1923, with the exception that in thesecond impregnation a compound is used having a slightly higher flowpoint than thaty described in the aforementioned application whichpermits the plug to be fabricated before the baking operation, since thecompound at the baking temperature will not tend to flow from theimpregnated section into they adjacent sections of the cable core andthereby reduce the efficiency of the plug. It suffices tosay that asection of the cable core is first treated with a relatively thinWaterproofing compound composed of a mixture of rosin oil and rosin andthe section is then subjected to a relatively heavy waterproofingcompound composed of rosin oil, rosin and asphaltum in which theasphaltum is the major ingredient so as to give the impregnatingcompound a sufiiciently high flow point. Y

After impregnatingthe section of the core which is to form the plug withthe water- .p proofing compounds above referred to, this section of thecore is preferably wrapped one or more times with elastic rubber tape 12with sufficient tension accumulatively .applied to the tape to bind thecable core into a very compact mass along two portions thereof indicatedby the numerals 13 and 14.

` In the embodiment illustrated in the drawing, only one tape l2 isshown applied to the core. Preferably a single tape 12 is appliedhelically to the core, beginning at either end of the section 11, and ifthis section is twelve inches in extent, it is first bound very tightlyfor four inches, then loosely for another four inches' along a 'portion15 intermediate the portions 13 and 14, and then very tightly again forfour inches, the intermediate por.` tion 15 being bound tightly enoughto reduce the diameter thereof as compared to the portions of the cablecore adjacent the ends of the section 11, but not as tightly as theporduring service and. wat r under pressure should pass either of theightly bound portions 13v and V14 thereof, the compound in the centerportion which is more or less mobile due to its character and itscomparative freedom to move in opposite directions, the latter being dueto the loose binding of the center portion lq'as compared to theadjacent portions 13 and 14, will be forced into the other` tightlybound portion thereby increasing the effectiveness thereof and providing a perfect seal for the adjacent portion of the cable core forpreventing .the entrance of water thereinto. A wrapplng of some'suitable strand, for instance cotton thread, is then applied helicallyto the core with suflicient tension at the beginning and ending of eachbound portion of the impregnated section as indicated by the numerals 16to retain the tape in position. The cable core is then inserted in asuitably heated baking oven where it is heated for a period sufficientlylong to expel any moisture which may be contained in the insulationofthe cable core. A filling material is used to build up the diameter ofthe core to approximately that desired. The filling material may be ofany suitable type which will beof a character to seal the space betweenthe outside ofthe tape 12 and the inside of a lead sheath 17 when thesheath is applied thereto and is preferably applied just previous to thesheathing operation and after fthe baking operation. Although thisrequires the stoppage of the press, it is of small consequence since thefilling material may be applied very quickly compared to the methodhereinbefore referred to wherein the entire plug is inserted during thestoppage of the press. Preferably, I employ for this purpose material ofthe type described and fully llt) disclosed in the copending applicationof F. S. Mahn, Seria'l'No. 331,360 filed April 11, 1923,` to whichreference may be had for a disclosure as to the particular ingredientsthereof. This material is composed of a .mixture of a plastic gum, suchas crude rubber, an adhesive material which will soften t-he gum, suchas a mixture of resin-and rosin oil, and a fibrous' filling material,such as asbestos fibers, and is of such a character that the heat of thelead sheath 17 when applied is sufficient to cause the Jsaid material',indicated in the drawings by the reference numeral 18,.to flow' into ahomogeneous mass to completely fill the space between 'the core and thesheath. When the lead sheath 17 is in place, a hemp coverin 19, a steelarmor 20, and an outer jute co ering 21 are applied in the usual manner.

By constructing a plug in accordance with be apparent.

the method hereinbefore described, a sealing compound having a maximumresistance to flow may be used for impregnating that section of thecable core to be plugged, and still retain a given amount offlexibility, due to the loose binding of the portion 15 as compared tothe binding of the portions 13 and 14 at either side thereof, as willreadily Also with the use of such a compound a plug is provided whichmay be inserted in the cable core before the baking operation, andconsequently the subsequent cable core sheathing operation may beaccomplished with a minimum of interruption to the operation of theextrusion press, in consequence of which a more durable and efficientsheath is produced.

What is claimed is:

1. The method of making a submarine cable, which consists in assemblinginto a cable core a plurality of insulated conductors, impregnating asection lof said cable core and compressing spaced portions of saidsection to form seals and to confine therebetween a mobile body ofimpregnating material whichl is forced toward one portion to increasethe effectiveness thereof upon the failure of the other portion toprotect the cable.

2. The method of making a submarine cable, which consists in assemblinginto a cable core a plurality of insulated conductors, impregnating asection of said cable core and compressing spaced portions of saidsection and a portion therebetween whereby one portion effectivelyfunctions in the event of failure of the other portion to protect thecable.

3. The method of making a submarine cable, which consists in assemblinginto a cable core a'plurality of conductors having a fibrous insulation,impregnating a section of said cable core, compressing a portion of saidsection, and further compressing to a greater degree the portions ateither side thereof, whereby .one portion effectively functions in theevent of failure of another portion to protect the cable.

4. The method of making a submarine cable, which consists in assemblinginto a.v

cable core a plurality of conductors having a fibrous insulation,impregnating a section of said cable core, and compressing a portion ofsaid section in such a manner that the diameter is Ireduced at aplurality of portions, an intermediate portion being greater in diameterthan the other reduced portions but smaller than that portion ofthe corenot Lreduced in diameter, whereby one portion effectively functions inthe event of failure of another portion to protect the cable.

5. The method of making a submarine cable,v which consists in assemblinginto a cable core a plurality of conductors having a fibrous insulation,impregnating a section of said cable core, compressing spaced portionsof said section `and aportion therebetween whereby one portioneffectively functions in the event of failure of the other portion toprotect the cable, subjecting the cable core thereafter to a dryingmedium to remove any moisture contained therein, thereafter building upthe compressed portions of said cable core to the size of theuncompressed portion thereof andsubsequently applying a sheath to thecable core.

6. In a submarine cable, a core comprising a plurality of conductorshaving a fibrous insulation, said core having an impregnated section,and a tape applied -to said section so that portions of said section ateither side of a central portion thereof are compressed whereby oneportion effectively functions in the event of failure of the otherportion to protect the cable.

7. In a submarine cable, a core comprising a plurality of conductorshavingv a fibrous insulation, said core having an impregnated section,and an elastic rubber tape applied helically to said section so that thediameter is reduced at a plurality of portions, an intermediate one ofsaid portions being greater in diameter than the other reduced portionsbut smaller than the remainder of the core whereby one portioneffectively functions in 4the event of a failure of the other portion toprotect the cable.

In witness whereof, I hereunto subscribe my name this 16th day of JuneA. D., 1925;

SAMUEL CLIFTON CAWTHON.

